Load stabilizing means for modulation systems



Jan. 14, 1941. DAWES 2,228,692

LOAD STABILIZING MEANS FORv MODULATION SYSTEMS I Filed on. 14, 1958 I5mm 'GOIIIZQIL. I

Patented Jan. 14,1941

mtmioaielsrs generally systems and l v devices formodulating radlo=frequency energy and,more particularlwtosystems in whichenergy 1 '1 f,modulated at difierent frequencies issupplied to 5 separate loads; y r.

V Inthe operationo'i systems oi thetypereferred todifferently-modulated. energy" may be supplied to two antennas forlrthepurpose or radiating two 1, differently modulated fieldswhich' overlapto provide-an equi signal zone which may beused as a guidancebeaconforaircraftr If the tworadiated fields are characterized,- bytdifierent modulation frequencieait is usual, practise-tosupply each ofthe ,twoxradiatmgg antennas with radio ,frequency '15 i energy from acommon source, rnodulating means I being interposed qlbetweenwthe'source and each i antenna n sls ne a fl t e type w a mechanicalmodulators ,Itf has 'beena foundpthat.{in systems" the "2'0:ener'gizi'ng' current each go f the antennas will vary from; zer to amaximum, ,suchva1iation bein t h n ina re' u n k1W3 variation of thepower in the load, will icausere ltidnin the tank tcircuit supplying;the antennas, fsuch "25 regulation being also attiremodulatingfrequency.

Inasmuch as the second antennais supplied with ;-radio' irequency energyfromthesouicernodulated :at a, second frequency it will be apparent thatregulation will also occur thej'input circuit at l 30 thissecondflfrequeney Thusl the energyfsupt J plied toeach antenna ismodulatedjnovonly at the intended frequency but also,1anddue to the Qregulationin the input circuit due' totheniodulation of theenergyisuppliedto theotherj antenna, 35 atj'the modulationf irequency ofthe energy suppliedto the other antenna. This eflect'is known ,as crossniodulation and in order as decreas'eor do "away with this 'efi'ect itthe usualpractise to t operate'thesystem at a. low fraction of itspossible output inorder to increase the ratio of the power intheinput-circuit to thepower drawn bysthe antennas-1 1 i it l Ihavefound that such or oss-modulation; may i lbe efiectively"decreasedor entirely prevented by providing 'iwitheach antenna anon-radiatingload which is suppliedwith power in a varyingamount which is equal rat'anytime totlie difference. be-

tween the load: -current drawn by the l associated antenna and theinstantaneous value. of "the current drawn by the antenna. 11,'I'hu s,the

1 dummygloadwill beconnected with the modulator in such a manner that,when the full power of the input'clrcuit is supplied to the antenna, nopower is. supplied to the dunimy;1oad,,this ratio. then lggwch'angingconstantlytthrcugh equality-until full PATENT-.2FFICEJ: t 1

mm srABmzINGMEANs-Forr W MQDULA'IION SISTEMSJ; l r H GomerflLDavies;,Wood side,"Mdaffassignor I flwashingtonglnstitute of'Technology,-'Inc'.,- WWnmEP -w sme i s s mmer t 3 Applicationbctobenld,1938, Serial No. 235,019 i her the entire Po sible poweroutput ofthe-source may be morenearly employed.

i i In prior artsystems, in which means-aecording Itothis invention arenot employed, and in which the :maximum power requiredto be-suppliedhtoeach antenna is, for example, 50 watts, (33 watts carrier,j100%modulated) it has been necessary totprovidega source having a possiblepower output of approximately 400 watts, ,the excess, or 300 watts,providing no useful purpose but beingnec- ,essary inordervtomaintainthe: required large. I ratio offpower'in theinput circuit topower inthe-1oad circuit In systems --employin'gthe-present invention it is, ofcourse, not-possibleto utilize the entire'power of the source intheantennas due to the power:absorbed-by the dummy loads, but themaintenance .of t a. constant load on thesource permitsa much largerfractionaof. thepower of 1 it thesource to be applied to the usefulloads] a It.is,accordingly;the object oftheinventionto provide anelectrical system for supp1yi ng-m0du- "lated radio frequency energyfrom a source. to 7 l twoor more loads, such as antennas, which system 7include-means -for maintaining a constant a load on the source, ofpower, thus preventing a crossmodulationl. a

xqOther objects-and features -of noveltywill be apparent from thefollowing description. andthe appended drawing, it being understood,however, lthatl-such description and drawing are only illustrative oitheinvention, which is not limited in a 1 way thereby or "otherwisethangby, the zip-"40 pendedclaims.

1 The single figure of the drawing is a diagran'r illustrating a beaconsystem incorporating means according to the invention.

In the single figure of the drawingthere is matrated a beacon systemeniployingfth'e load stabilizing means of the present invention. In this7 systema tank circuit I, whichiorms'theffinal stage of a source ofradio irequencyenergy, isconnected to supply energy to two useful loads2," 3 which; maybe antennas adapted'to radiate fields winch overlap toprovide .anequi-signal 'zone which may be used asa guidance 'means foraircra ft, .-The outputcoil 4 of the tankicircuit :is

coupled to two coils 5, 6. Each ofthese coils is connected to supplyenergy-to one of the useful loads,modulating means being connectedbetween each of such coils and associated useful load in order that theradio frequency energy in each such useful load will be modulated at acharacter istic frequency. l v

One of theoutput terminals of coil 5 is -connected to two shieldedtransmission lines'lfl, 'II and the second terminal of the coil isgrounded at I! through the shields of the two lines. The line H isconnected to supply current to the useful load 2, while the secondtransmission line lll' isconnectedto supply current to a dummyload l3]the purpose of which will be made apparent hereinafter.

Mechanical modulating means are'connected in the transmission lines H),II in order to impress a characteristic modulation on the .radiofrequency energy supplied to thetwo loads. Such means -comprise a rotarycapacitor including the two stator plates l4,w|5, which are connected,re-

spectively, to the transmission lines l0, ll by shielded transmissionlines I6, l1, and-a rotor I8 which is grounded at H! and which hasplates at the opposite ends thereof which pass over .the stator platesas the rotor is operated. Shortcircuited tuning stubs 20, 2| are alsoconnected to transmission lines Ill, H and provide means for controllingthe reactance at the point of connection of the modulating means to thetransmission lines when a condition of maximum impedance obtains at thatpoint; It will b'e'seen that the movement of the rotor will cause theplates thereof to pass the two stator plates and alternately andprogressively short-circuit the .two transmis-. sion' lines to ground atIf! through these stator plates. v 'In the operation of the modulator14, I5, Hi,

When, the rotor is in the position illustrated, with the one platethereof entirely covering the stator plate 14, transmission linell willbe short-circuited to ground at I9 and will not pass any current totheload 2. Atthe same time currentwill flow from coil 5 throughtransmission line l0 directly to load 13, the modulator not drawing anycurrent from line ID at this time. As the rotor I8 continues itsmovement, the one plate thereof will pass away from stator plate l4,thereby causing-an increasing amount of current to be drawnthroughline'll tothe useful loadZ, while I plied to the useful load.

It will be seen that the radio frequency'energy output of the sourcewill be supplied to the useful and passiveloads in. amounts which willvary .in accordance with the size and positioning of the stator androtor plates and that the frequency of the supply of maximum or minimumcurrent to either of the loadswill be determined by the speed of therotor and the number of the rotor and stator plates. The two loads willtherefore be supplied with current at the same radio frequency,modulated equally but with opposite sign,

whereby the total power supplied to the two loads willremainsubstantially constant.

A dummy load is associated with load 3 in the same manner as describedhereinbefore with respect to dummy load 13 and useful load 2, and radiofrequency energy is supplied' to' these two loads through transmissionlines 3|, 32, respectively. Tuning stubs 33, 34 are connected to thetransmission lines for a purpose which is identical with that of stubs20, 2|. Modulating means comprising a rotary capacitor including thestator plates35, 36 and the rotor 31 are provided and are I operable, inthe same manner as the means described hereinbefore, to vary the powersupplied to the two loads 3 and 30 in such a manner that the powersupplied to the passive load 30 at any instant will be equal to thedifference between the maximum amount of power drawn by the usefulload.3 and the instantaneous power drawn by the load3, whereby, thetotal power supplied to-thetwo loads remains constant. In order tomodulate the energy'supplied touseful load 3 at a characteristicfrequency different from the modulationfrequency of the energy suppliedto load 2,-the rotor 31 may be constructed in the same manner as rotorl8 and driven at a-different speed, or, as illustratedin the drawing, itmaybe provided with three .or

more plates and, accordingly, may be driven at 'the same'speed-as therotorlB. i Y

It will 'be seen that, by theprovision of the dummy loads and by theenergization of eachof these in such a manner that the powersuppliedthereto always has the described relation to the power supplied to theassociated useful load, the

total power drawn by each branch of-the system disclosed will bemaintained-constant'andthe total power-drawn from-the source I willtherefore be constant, whereby it is possible to utilize a greaterfraction of the possible output of the source in the useful loads.--' I"While I have illustratedand described one embodirnent of my invention,it will be apparent to .those skilled in the art that further improve-'ments and modificationsthereofmay be-made without departing in any wayfrom the spirit or scope of the invention, for the limits of which.referencemust be had to the appended claims.

- Whatliclaim is: I l 1 1. 'An electrical system for supplying modulatedradio frequency energy to a plurality of useful loads such asantennasrcomprising a source of energy, a plurality of useful loads,

transmission lines connecting each of said loads to the source, anon-useful load associated with eachuseful load, transmissionlinesconnecting each of said non-useful loads to the source, means associatedwitheach useful load and its.

associated non-useful load for modulating the energy supplied theretoand comprising means for alternately and progressivelyshort-circuitingto ground energy from the transmission lines connecting the useful andnon-useful loads to the source, in such amounts that the energy suppliedto any non-useful-load' at'any instant is approximately equal to thedifferencev between the maximumenergysupplied to the associated usefulload and the instantaneous energy supplied thereto. w I a 2. Anelectrical system comprisinga-source of radio frequency energy, 'a'plurality of useful loads such as antennas connectedthereto, means fordifferently varying the amounts of energy supplied by said source.tosaid useful loads, a plurality of non-useful loads each of which is associated with one of said useful loads and is connected to the source,.means for varying the amount of energy supplied to each of saidnonuseful loads, the means for varying the energy supplied to eachuseful load and to its associated non-useful load comprising spacedconducting members connected respectively to the connections between thesource and the useful load and

